Data for Virtual Globe Developers

Natural Earth - Vector and raster map data at 1:10m, 1:50m, and 1:110m scales. Very well presented. Try GIMP if you need to modify the TIFF files.

DIVA-GIS - Vector and raster data organized per country. Shapefiles for boundaries, water, roads, and railroads. Raster data for elevation, land cover, population, climate data. I have not used their raster data but it sure sounds interesting.